Rivers and lake systems in the southern cone of South America have been widely influenced by historical glaciations, carrying important implications for the evolution of aquatic organisms, including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes (Odontesthes) in the region comprise a radiation of 19 marine and freshwater species that have been hypothesized on the basis of morphological or mitochondrial DNA data to have either transitioned repeatedly into continental waters from the sea or colonized marine habitats following freshwater diversification. New double digest restriction-site associated DNA data presented here provide a robust framework to investigate the biogeographical history of and habitat transitions in Odontesthes. We show that Odontesthes silversides originally diversified in the Pacific but independently colonized the Atlantic three times, producing three independent marine-to-freshwater transitions. Our results also indicate recent introgression of marine mitochondrial haplotypes into two freshwater clades, with more recurring instances of hybridization among Atlantic- versus Pacific-slope species. In Pacific freshwater drainages, hybridization with a marine species appears to be geographically isolated and may be related to glaciation events. Substantial structural differences of estuarine gradients between these two geographical areas may have influenced the frequency, intensity and evolutionary effects of hybridization events.

中文翻译：

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线粒体和基因组RAD数据揭示的南美银边鱼类辐射中的生物地理学，栖息地转变和杂交。

南美洲南锥体的河流和湖泊系统受到历史冰川的广泛影响，对水生生物的进化具有重要意义，包括促进海洋和淡水生境之间的过渡，以及通过水路连通性和溪流捕获触发初期物种之间的杂交事件。该区域的银边鱼（Odontesthes）包含19种海洋和淡水物种的辐射，这些辐射已根据形态学或线粒体DNA数据进行了假设，在淡水多样化后已从海中反复过渡到大陆水域或定居的海洋栖息地中。此处介绍的新的双酶切限制酶切位点相关的DNA数据提供了一个可靠的框架，可用来研究牙形目的生物地理历史和栖息地转变。我们表明，Odontesthes银边最初在太平洋地区多样化，但独立地殖民了大西洋三遍，产生了三个独立的从海洋到淡水的过渡。我们的研究结果还表明，海洋线粒体单倍型最近进入了两个淡水进化枝，大西洋和太平洋坡种之间杂交的杂交实例更多。在太平洋淡水排水系统中，与海洋物种的杂交似乎在地理上是孤立的，并且可能与冰川事件有关。这两个地理区域之间河口梯度的实质性结构差异可能影响了频率，